The yeast pheromone response provides an excellent model both for G protein mediated signalling as well as adaptation. We propose to use a combination of genetic and molecular approaches to identify and characterize elements involved in both processes. Mutational analysis will be used to perform a structure/function analysis of the subunits of the G protein. Assays involving guanyl nucleotide metabolism and subunit interaction will be established for this purpose. A number of genetic screens will be employed to identify elements in both the signalling and adaptive pathways. It is hoped that the effectors for these pathways can be identified via these screens. Once genes encoding signaling elements have been identified, recombinant DNA methods will be used to express them in bacteria so that immunogenic quantities can be purified for antibody production. These antibodies will serve as reagents for cytological and biochemical studies of the signalling elements. The intention of this research is to provide a comprehensive description of cell surface receptor mediated signalling from its inception at the plasmid membrane to the effector pathway ultimately responsible for controlling gene expression.